LinkedIn, the online network geared to professionals, has surpassed slumping Myspace as the second-most popular online social network in the U.S. in terms of Web traffic, behind Facebook.

LinkedIn had 33.9 million unique visitors in June, an increase of about half a million from the month before, according to new data from comScore, the Internet analytics firm. By contrast, fewer than 33.5 million Americans visited Myspace last month, a drop of about 1.4 million U.S. visitors from May.

The numbers don't tell the whole story -- Myspace still has an estimated 130 million active users, compared with roughly 115 million for LinkedIn -- but it's another symbolic blow to the once-dominant social network, which is struggling to reinvent itself.

U.S. traffic to Myspace is half of what it was in June 2010, when the site had more than 66 million unique visitors, according to comScore. Myspace still leads third-place Twitter, which had 30.6 million visitors last month, although at their current rates, Twitter will eclipse Myspace in the next few months.

By comparison, Facebook, social networking's ever-expanding behemoth, had 160.8 million unique visitors in June.

A new survey sheds some light on how are people using LinkedIn, which lets members post résumés, search for jobs and network with other professionals in their fields.

According to a survey of 500 LinkedIn users by Lab42, a market-research firm, 35% of members visit the site daily, and 42% update their profiles regularly. Perhaps not surprisingly, the survey found that top-level executives and entry-level workers use LinkedIn differently: The younger members use the site mostly to find jobs, while the senior executives use it for networking and promoting their businesses.